Researchers said nursing homes must help residents maintain clean teeth and dentures because germs found in dental plaque can make their way into the lungs and cause deadly pneumonia in elderly residents, according to a new study report.

U.S. researchers said they found clear evidence in eight patients who developed pneumonia while in the hospital that the condition was caused by their own dental plaque. This is the first time research has been able to find a link between dental hygiene and respiratory infection, according to lead researcher Dr. Ali El-Solh of the University at Buffalo in New York.

For the study, which is published in the latest issue of the Chest, researchers tested 49 nursing home residents who were admitted to a nearby hospital with a high risk of pneumonia and made molecular “fingerprints” of the bacteria found in each patient’s mouth before he or she developed pneumonia.

Of the 49 patients, 28 had germs known to cause respiratory disease in their dental plaque samples. Of the 14 who eventually developed pneumonia, 10 of them had started out with respiratory disease-causing germs in their teeth.